Preheat the grill and set the tray about 15cm from the grill. Line a baking tray with aluminium foil.
Using a mortar and pestle or spice grinder, grind the peppercorns, chopped garlic, lime rind and salt until the peppercorns are finely ground. Rub salmon fillets with olive oil, then place onto the prepared tray, skin side down. Rub spice mixture onto top of salmon fillets.
Grill until the salmon is flaky and no longer pink in the center, 10 to 15 minutes. Drizzle with soy sauce and serve.
If these aren't in your local supermarket you can get them from Asian shops or supermarkets.